The present invention relates to a method and apparatus for controlling a photo printer such as a laser printer, and particularly relates to an improvement of a method and apparatus for controlling a photo printer in which a bit map memory having a large capacity which has been conventionally used only for printing can be used in other uses.
Examples of photo printers include a laser printer, a liquid crystal printer using a liquid crystal shutter array, and the like. Although being applicable to any kind of photo printers, the present invention will be described in connection with a laser printer by way of example. Prior to the description of the present invention, a prior art laser printer control apparatus will be described in reference to the drawings. FIG. 1 is a block diagram showing the whole arrangement of the conventional laser printer control apparatus.
In FIG. 1, the laser printer control apparatus is provided with: an MPU 1 for controlling the laser print operation; a host computer 2 (hereinafter simply referred to as "host") for transmitting printing data to a laser printer; a reception FIFO 3 having a buffer function for storing the data transmitted only from the host 2; a line memory 4 for storing the data stored in the reception FIFO 3 by line (text data provided with a control code for indicating for example carriage return attached at the line end); a bit map memory 5 having a large capacity of bits corresponding one to one to a print dot pattern to be printed on a paper 13 expressed by the data in the line memory 4; a laser printer printing portion 6, that is, a printing mechanism for printing the dot data in the bit map memory 5; a laser printer interface 7 for converting the parallel data read out from the bit map memory 5 into serial data so as to transmit the serial data to the laser printer printing portion 6; an ROM 8 for storing a program to be executed by the MPU 1; a character generator ROM (CGROM) 9 used for developing the data stored in the line memory 4 into the bit map memory 5; a cable 11 for transmitting the data of the host 2 to the reception FIFO 3; and an internal bus 12 for transmitting data, control signals, etc. between the MPU 1 and the constituent elements. A laser printer control circuit 10 is formed of the constituent elements 1, 3 through 5, 7 through 9, and 12. A laser printer 100 is formed of the laser printer circuit 10 and the laser printer printing portion 6.
FIG. 2 is a flow-chart showing the printing operation performed by the control apparatus 10 shown in FIG. 1. Referring to FIGS. 1 and 2, the operation of the conventional laser printer control apparatus will be described hereunder.
In FIG. 1, the data transmitted from the host 2 is stored in the reception FIFO 3. In a step 20 of FIG. 2, whether there is data in the reception FIFO 3 or not is judged. If there is data, the operation is shifted to a step 21 of FIG. 2. When the data, does not include any developing command such as a carriage return command (CR), a line feed command (LF), or the like, the operation is shifted to a step 22 in which the data is transferred to the line memory 4 in FIG. 1. When a developing command such as a line feed command, a carriage return command, or the like, is present in the data transmitted from the host 2, data in the line memory 4 is converted into a printing dot pattern data corresponding to the data and developed into a bit pattern in the bit map memory 5 corresponding to the dot pattern (a step 23). The dots in the dot pattern correspond one by one to the bits in the bit pattern. Further, when there is a print command, such as a page feed command (FF), or the like, in the data transmitted from the host 2, the operation is shifted to a step 24 in which the dot data in the bit map memory 5 is transferred to the laser printer 6 so that the dot pattern is printed by the laser printer 6 (in a step 25).
The prior art concerned with the laser printer control apparatus is disclosed, for example, in "NIKKEI ELECTRONICS", published Apr. 8, 1985, (pages 143 through 146).
The arrangement and operation of the conventional laser printer control apparatus have been described above in reference to FIGS. 1 and 2. However, the data transmission in the conventional apparatus of the kind described above is carried out by a one-way transmission system in which the data-transmitted from the host 2 is merely transferred to the printer 100 and the bit map memory 5 is left in an unused state except during the printing time.
However, the bit map memory 5 used in the laser printer control apparatus 10 has a large capacity of about 1 M bytes in order to improve the resolution of the printed dot pattern. Accordingly, if the bit map memory 5 having such a large capacity used only during printing can be used employed for other uses, the apparatus of the kind described above can be effectively put to practical use. For example, the host connected to the printer uses a memory having a large capacity to carry out processing such as numerical calculation, external-character formation, and the like, and therefore the capacity of the memory in the host becomes insufficient frequently.